a[n] = 1 - 1/a[n-1]
= (a[n-1]-1)/a[n-1]
a[n+1] = 1 - 1/a[n]
= 1 - a[n-1]/(a[n-1]-1)
= - 1/(a[n-1]-1)
a[n+2] = 1 - 1/a[n+1]
= a[n-1].
∴ a[n+3] = a[n]
∴ a[2009] = a[2] = 1 - 1/a[1] = 1/2.
应该没有错吧``` .
a[n] = 1 - 1/a[n-1]
= (a[n-1]-1)/a[n-1]
a[n+1] = 1 - 1/a[n]
= 1 - a[n-1]/(a[n-1]-1)
= - 1/(a[n-1]-1)
a[n+2] = 1 - 1/a[n+1]
= a[n-1].
∴ a[n+3] = a[n]
∴ a[2009] = a[2] = 1 - 1/a[1] = 1/2.
应该没有错吧``` .